This invention relates to a device for passing through pipelines. It can take many forms, some of which are called a pipeline `Swab` or `pig`. Such a known device which is usually generally cylindrical in shape, but is sometimes spherical, is used for a variety of purposes in pipelines. For example, removing loose debris, diameter gauging, expelling gases or fluids, stopping off, separating different gases or fluids, etc. It can be caused to pass through a pipeline also by variety of methods, e.g. by towing, by gas or fluid pressure in the pipeline, or it may be self-propelled. The device according to the invention can also be used for these and other purposes, and can be moved by the same methods.
Known devices suffer from a number od defects and difficulties. It is often difficult to insert them in and remove them from a pipeline, since they must of necessity be of a diameter close to or slightly greater than that of the pipeline. They do not always form a perfect seal in the pipeline if the latter includes substantial variations of internal diameter. In order to ensure a seal, the swab or pig must have a frictional contact with the wall of the pipeline, but the better the seal the greater the difficulty of propelling the device, and the greater the difficulty of insertion without special means attached to the end of the pipeline.